Control system for clothes dryers



May 1, 1962 v. J. KUROWSKI CONTROL SYSTEM FOR CLOTHES DRYERS 3Sheets-Sheet 1 Filed July 9, 1959 INVENTOR. J. Ku Rows K I F l G. i

HIS ATTORNEY May 1, 1962 v. J. KUROWSKI CONTROL SYSTEM FOR CLOTHESDRYERS 3 Sheets-Sheet 2 Filed July 9, 1959 INVENTOR. VICTOR 3'.KUROWSYKI H15 ATTORNEY May 1, 1962 v. .1. KUROWSKI CONTROL SYSTEM FORCLOTHES DRYERS 5 Sheets-Sheet 5 Filed July 9, 1959 F'IG.4

INVENTOR VICTOR J. KUROWSK\ H l 5 ATTORNEY United States Patent IGNTRGLSYSTEM Edi CLQTHES DRYERS Victor .l'. Kurowshi, Louisville, Ky.,assignor to General Eiectric tjornpany, a corporation of New York Fiied.luly s, 1959, fier. No. $25,972 it Claims. (Cl. 34--45) My inventionrelates to clothes drying machines, and more particularly to automaticcontrol systems for use in such machines for controlling the dryingoperation.

The wide variety of modern fabrics used in the manufacture of clothingha resulted in the fact that a substantial spread of drying temperaturesrepresent the optimum for vmious fabrics. Experience has shown that themore delicate fabrics which are best dried at lower temperatures arealso generally those which dry more quickly. For instance, nylon andDacron clothing is best dried at relatively low temperature, butnonetheless it dries much more rapidly than cottons such as sheets andtowels, even though the cottons be dried at a substantially highertemperature. Because of these factors, it is highly desirable thatdrying cycles for the more delicate fabrics provide for relatively lowtemperatures and that the longer drying cycles desirable for the dryingof cottons provide higher drying temperatures. However, while it isdesirable that materials such as cottons be dried at highertemperatures, it is also desirable that these temperatures be decreasedtoward the end of a drying cycle so that the clothes may be morecomfortably handled after the drying sequence is finished and they arebeing removed from the machine.

It has been found that the foregoing, as to the desirability of a spreadof drying temperatures which varies proportionately with the dryingtime, holds true whether the dryer be of the straight timed variety orof an automatic cycle type such as those where the total time of thecycle is controlled jointly by the timer mechanism and by a thermostaticdevice.

To summarize, it is desirable that where the material to be dried issuch that it requires only a short cycle, a low temperature dryingoperation be provided and that the temperature of the drying beincreased as the type of clothing requires a longer cycle. A furtherfactor to be considered is the desirability of decreasing the drying tenperature towards the end of the drying cycle to improve the ease ofhandling the clothes.

it is therefore an object of my invention to provide economical meansfor providing relatively low drying temperatures for short cycles andrelatively high drying temperatures for the longer cycles.

A further object of the invention is to achieve this effect by suitablevariation of the heating effect of a biasing heater positioned inheating relation to a main thermostat arranged to sense the temperatureof clothes in the drying machine, and to achieve this variation by meansof a timer control mechanism.

A more specific object of the invention is to achieve this variation ofthe heating effect of the biasing heater by providing at least tworesistances in parallel with each other with a switch in at least one ofthem, with means controlled by the timer mechanism for opening theswitch when a relatively long cycle is selected so that a higherresistance is in series with the biasing heater which is consequentlyless effective; when the biasing heater is less eifective the mainthermostat requires more heat from the clothes before it trips, and thusthe opening of the switch causes a higher temperature drying operationto be provided by the selection of a longer drying time.

Yet a further object of the invention is to provide an improved controlarrangement whereby longer drying cycles, which call for relatively hightemperatures to start with, provide for a decrease in the temperature asthe 3,031,768 Patented May 1, I962 cycle continues in order tofacilitate handling of the clothes at the end of the cycle.

In carrying out my invention in one form thereof, I provide a clothesdrying machine which has a conventional clothes container with a mainheater positioned to heat the clothes in the container. Thermostaticmeans are positioned to be responsive to the temperature of the clothesin the container, and are also acted on by an electric resistance-typebiasing heater which is positioned in suitable heating relation to thethermostatc means. When the thermostatic means senses a predeterminedhigh temperature, due to the combination of the clothes temperature andthe biasing heater, it causes a first switch to open to stop operationof the main heater. As thus far described, it is clear that the moreeffective the biasing heater, the lower the clothes temperature whichwill trip the thermostatic means.

In series with the biasing heater I provide at least two conductorsconnected in parallel with each other, with a second switch member inone of the two conductors. The resistances in the conductors are suchthat with the sec ond switch open a higher resistance is presented bythe two conductors, and with the second switch closed a lower resistanceis provided by the two conductors.

Manually presettable control means are provided for variably limitingthe length of operation of the main heater. The control means, inaddition, moves the second switch means to an open position when thecontrol means is set for a relatively long period of operation and to aclosed position when set for a relatively short period of operation. Inthis manner the biasing heater has a smaller effect on the thermostaticmeans when a long operation is selected and a relatively large eifect onthe thermostatic means when a short operation is selected. The netresult of this is to cause high temperature drying automatically inresponse to selection of a long timer operation and low temperaturedrying in response to selection of a short timer operation.

As well as having the timer control open the second switch means whenmoved to provide a selectively long cycle, the timer may readily bearranged to cause the second switch to close when the time decreasesback to that provided for delicate loads. As a result, even if a longcycle is selected the clothes temperature will decrease toward the endthereof to facilitate the handling of the clothes when the cycle comesto an end.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention, however, both as to organization and methodof operation, together with further objects and advantages thereof, maybe best understood by reference to the following description taken inconjunction with the accompanying drawings.

In the drawings, FIGURE 1 is a side elevational view of a clothes dryerincorporating my improved dryer control arrangement, the view beingpartly broken away and partly sectionalized to illustrate details;

FIGURE 2 is a horizontal sectional view of the drye with certainsurfaces broken away and partly sectionalized to illustrate furtherdetails;

FIGURE 3 is a schematic illustration of my improved control circuit; and

FIGURE 4 is a cam chart showing the sequence of operation of the camcontrolled switches of FIGURE 3.

Referring now to FIGURES l and 2 of the drawings, I have shown therein adomestic clothes dryer 1 including a clothes tumbling container or drum2 provided within a suitable outer casing or cabinet 3 which completelyencloses it on all sides. The drum is mounted for rotation withincabinet 3 on a substantially horizontal axis, and is generallycylindrical in shape, having a first outer Wall portion 4, second andthird outer wall portions and 6 located respectively adjacent the endsof the drum, a back wall 7 and a front wall 8. Outer wall portions 4, 5and 6' are imperforate over their entire length, so that the entireouter shell of the basket is imperforate; on the interior surface ofcentral portion 4 there is provided a plurality of clothes tumbling ribs9.

The front of drum 2 is rotatably supported Within the outer casing 3 bymeans of a pair of idler roller wheels it) and 11 which are rotatablysecured to the top of an upwardly extending member 12 secured at itsbottom to the base 12a of the machine (FIGURE 1). It will be observedthat rollers and 11 are disposed beneath the drum in contact withportion 6 thereof. The rear end of the drum receives its support from aroller wheel 13 which is positioned beneath portion 5 of the drum insupporting and frictionally driving engagement therewith.

Roller 13 is mounted on a shaft 14 supported in bearings 1'5. Shaft 14is secured to a pulley 16 which is driven from a belt 17 in turn poweredby a pulley mounted on the end of a shaft 19 of an electric motor 20.The motor, pulleys, and roller 13 are so proportioned to drum 2 and toeach other that drum 2 is rotated by roller 13 at an appropriate speedto provide tumbling action for articles of clothing placed therein.

in order that a stream of drying air may be introduced into and passedthrough the clothes drum, the drum is provided with a central aperture21 in its front wall 3 and with a plurality of perforations 22 extendingin an annulus around back wall 7. Rigidly secured to the rear wall 23 ofcasing 3 by any desired means such as, for instance, welding at suitablepoints 24, is a bathe member 25 which has secured thereto heating means26 appropriately insulated from the battle member. Heating elements 26may be annular in shape so as to be generally coextensive with theperforations 22 in drum 2. A baffie member 27 is rigidly secured to theback wall 7 of the drum outside the ring of perforations 22 and withinthe stationary bafile 25 so that an annular air inlet 23 is, in effect,formed by the two baflles 25 and 27. Baffle 27 is further provided withan annular series of openings 29; in this manner a passage is providedfor air to enter annular opening 28 between the bafides, pass over theheating elements 26, through openings 29 and then through perforations22 into the interior of drum member 2.

In addition to the air guiding function, the bafiles 25 and 29 help therollers 19, 11 and 13 support the drum 2. Secured to the central portion3G of baffie 27 is a bracket 31 to which in turn is secured a stub shaftmem- L ber 32 arranged substantially coaxial with drum 2. The centralportion 39 of baffie 27 has an opening 34 formed therein in the form ofa slot. The slot is suitably formed (as more fully described inapplication S.N. 789,869 filed January 29, 1959 by William F. Simpsonand assigned to the same assignee as this invention) so as to permitstub shaft 32 a limited amount of movement in the vertical direction butvirtually no movement in a horizontal direction. -Thus, the slightvertical motions of the drum which result from the tumbling of theclothes can be accommodated While at the same undesirable horizontalmotion is afiirmatively prevented by the engagement of stub shaft 32 inslot 34.

The front opening 21 of the drum is substantially closed by means of astationary bulkhead generally indicated by the numeral 35. Bulkhead 35is made up of a number of adjacent members including the inner surface36 of an access door 37 mounted on the dryer cabinet, a stationary frame38 for the door, the inner surface 39 of an exhaust duct 40, and anannular flange 41 mounted on the frame 38 and on the duct wall. It willbe noted that a suitable clearance is provided between the inner edge ofthe drum opening 21 and the edge of bulkhead 35 so that there is norubbing between the drum and the bulkhead during rotation of the drum.In order to prevent any substantial air leakage through opening 21between the interior and the exterior of the drum a suitable ring seal42, preferably formed of felt-like material, is secured to flange 41 insealing relationship with the exterior surface of drum wall 8.

Front opening 21, in addition to serving as part of the air flow paththrough the drum, also serves as a means whereby clothes may be loadedinto and unloaded from the drum. The door 37, whose inner surface formspart of the bulkhead closing the opening, is mounted on cabinet 3 andwhen the door is opened clothes may be inserted into or removed from thedrum through the door frame 38. It will be noted that the door includesan outer flat imperforate section 43 and an inwardly extending hollowsection 44 mounted on the flat outer section. Hollow section 44 extendsinto the door frame 38 when the door is closed, and the door surface 36which comprises part of the combination bulkhead 35 is actually theinner wall of this hollow section.

The air outlet from the basket is provided by a perforated opening 45formed in the inner wall as of hollow door section 4-4. The bottom wallsection of door 34 and the adjacent wall of door frame 3% are providedwith aligned openings 46 and 47, opening 47 providing the entrance toduct 4%. As shown, a lint trap '48, which may comprise a fine mesh bag,is preferably positioned in exhaust duct 44? at opening $7, the bagbeing supported by the door frame 38.

Duct 4i) leads to suitable air movingmeans which may, as shown, comprisea centrifugal blower 49 mounted on the motor shaft and thus driven bymotor 2i The outlet of blower 49 communicates with an outlet duct 50(FIGURE 2) which extends to an opening 51 in the back 23 of cabinet 3.During operation of motor 263, the rotation of blower 49 causes air tobe drawn into cabinet 3 through a suitable opening 51a, through annularopening 28, over heaters 26, through openings 29 and perforations 22into drum 2, across the drum, through perforated opening 45 and alignedopenings 46 and 4-7 into duct 4% and then through the blower 49, theoutlet duct so, and opening 51 to atmosphere.

The operation of the dryer 1 is controlled by a new and improved controlsystem, one embodiment of which is shown in the circuit diagram ofFIGURE 3. As shown there, the entire control system of the machine isenergized across a three wire power supply'system including supplyconductors 52 and 53 and a neutral conductor 54. For domestic use, theconductors 52 and 53 will normally be connected across a 220 volt powersupply with 110 volts appearing between the neutral line 54 and each ofthese conductors.

The drive motor 2e includes a main winding 55 and a start winding 56which are connected in parallel with each other between supply conductor52 and neutral conductor 54. Specifically, the circuit, starting atsupply conductor 52, passes through a switch 5'7, then through thewindings 55 and 56 in parallel with each other, a standard motorprotector device 58, a switch 59 positioned (FIGURE 1) to be opened whenthe door 37 is opened and closed when the door is closed, and neutralconductor 54. Included in the parallel branch circuit of auxiliarywinding 56 is a switch 60 controlled by a centrifugal mechanism 61rotatable with the motor; when the motor comes up to a certain speedupon energization of the windings 55 and 56, the device 61 will causeswitch 60 to open thereby de-energizing winding 56 and permitting themotor to continue running on winding 55 alone.

Returning to switch 57 which is in series with both windings of themotor, this switch is under the control of a cam member 62 which in turnis driven by a timer motor 63 when energized. The timer motor 63 alsocontrols cams 64, 65 and 66 which respectively control switches 67, 68and 69. As well as being driven by the timer motor 63 when energized,the cams 62, 64, 65

and 66 are manually presettable to a desired position by means of acontrol member 70 which is generally provided in a readily accessibleposition such as for instance, as shown in FIGURE 1, on the backsplasher71 secured to the top of cabinet 3 of machine '1. As also shown inFIGURE 1, the timer motor 63 and the cams and switches controlledthereby form together a control assembly 72 which is generallypositioned within backsplasher 71 as shown. The energizing circuit fortimer motor 63, starting with supply conductor 52, passes through switch67, a switch 73 controlled by centrifugal mechanism 61 and closedthereby at the same time that switch 6t is opened, a main thermostaticdevice 74, preferably in the form of a bimetal element as shown, andtimer motor 63, to conductor 54. The bimetal thermostatic means has ahigh temperature trip position in which it moves into engagement *with acontact 75 and a low temperature reset position in which it moves intoengagement with a contact 76. The circuit through the timer motor 63 iscompleted when element 74 engages contact 75. Alternatively, whenelement 74 engages contact 76, a circuit is completed, starting atsupply conductor 5'2, through switches 67 and 73, bimetal element 74,contact 76, protective device 77, and the heaters26 to conductor 53.

It will be observed in FIGURE 1 that the thermostatic device 74 ispositioned at the front of the dryer on the bulkhead 35 directly belowthe air outlet 45 from the drum. The thermostatic element 74 iseffective to sense the temperature of the exhaust air leaving the drum,which temperature is very close to the actual clothes temperature. Inaddition to the clothes temperature as a factor affecting the operationof thermostatic means 74, a biasing heater 78 is provided in closephysical relationship with element 74 so as to be in heating relationthereto. The heater 78 is of relatively high resistance compared toheater 26 (for instance, approximately 110% ohms for heater 73 and ohmsfor heater 26 may be provided) so that its power consumption compared tothe main heater is exceedingly small. In fact, the small size of heater78 and the desirability of having it close to the thermostatic element74 generally causes the preferred construction, in practice, to providefor a unitary assembly within a single casing, which assembly includesboth the biasing heater 78 and the thermostatic element 74.

The biasing heater 78 is energized through a circuit which, starting atconductor 52, extends through a first group 79 of parallel connectedconductors, a second group 80 of parallel connected conductors in serieswith the first group 79 and the biasing heater, the biasing heater 78itself, and neutral conductor 54.

The first group 79 includes three conductors 81, 82 and S3. Conductor 81has therein a relatively high resistance 84, conductor 82 has therein asmaller resistance 85 in series with switch 69, and conductor 83 has thesmallest resistance which may be simply its own almost negligibleresistance, together with switch 68 therein. It will be clear that whenboth switches 68 and 69 are open the circuit for biasing heater 78 mustof necessity pass through resistance 84; this has the result thatrelatively little voltage drop occurs across the biasing heater 78 whichtherefore does not provide as much heat as it would if a smallerresistance were in circuit with it. Of course, the less heat provided bybiasing heater 78, the more heat must be provided by the clothes in drum2 for thermostat 74 to trip so that in effect the opening of switches 68and 69 has the efiect of increasing the clothes temperature which causestripping of thermostat 74.

If switch 68 is maintained open but switch 69 is closed, then a smallerresistance 85 is available as an alternative path for the energizingcircuit of biasing heater 78, more power will be available to thebiasing heater, and it will furnish more heat to thermostat 74 so thatless heat from the clothes is necessary for tripping of the thermostat.In the same manner, closing of switch 63 provides in effect a shortcircuit across conductors 81 and 82 through which the energizing circuitfor heater 73 will pass. With this arrangement the heater 78 willreceive a maximum of power, and the temperature of the clothes whichcauses tripping of thermostat 74 will be at a minimum.

Referring now to group of parallel connected conductors, it includesthree conductors 86, 87 and 88. Conductor 86 includes a relatively highresistance 89, conductor 37 has a lower resistance 9%, and the thirdconductor 88 has a very small resistance which may be simply its own. Inseries with the resistances in conductors 87 and 88 are a pair ofthermostatically responsive devices 92 and 93 respectively which may, asshown, he simply small bimetallic cantilever switch arms. Thermostats 92and 93 are positioned, as shown in FIGURE 2, to be responsive to theambient temperature, that is, to the temperature of the air surroundingthe dryer which will be drawn into the dryer by the blower for heatingand circulation through drum 2. Thermostats 92 and 93 are calibrated sothat they each close at a different ambient temperature; the thermostat92 closes at the higher temperature, preferably on the order of 90 F.,while the other thermostat 93 closes at a substantially lowertemperature, which may be on the order of 70.

With this arrangement a relatively high ambient temperature causes arelatively high clothes temperature to be required before thermostat 74trips, and the clothes temperature required to efiect tripping decreasesas the ambient temperature decreases and the small secondary thermostatsclose. The construction providing the ambient temperature compensation,while described herein to provide complete understanding of a completeand operative control circuit, does not form part of my invention but isthe specific invention of Donald W. Lynch and is claimed in hisapplication SN. 825,976 filed concurrently herewith (now Patent3,009,256 issued November 21, 1961) and assigned to General ElectricCompany, assignee of the present invention.

For a more complete understanding of the invention, let it now beassumed that a load of ordinary cottons is to be dried, and that themachine is located. in a room where the temperature of the air to bedrawn into the machine is 75. With an average type load such as ordinarycottons, the user sets the dial 70 so that approximately two thirds ofthe time available is provided. At this setting, as can be seen byreference to FIGURE 4, switch 69 is closed by cam 66 and switch 68 isopened by cam 65; also, with a temperature of 75, thermostat 93 is openand thermostat 92 is closed. In addition, since the cycle is juststarting, the main thermostat 74 is in its cool or reset position whereit engages contact 76 to provide an energizing circuit for the heaters26 and to prevent the timer motor 63 from operating.

It will further be observed from FIGURE 4 that the operation of manualmember 76 also causes closing of switches 57 and 67 and, provided thedoor is closed so that switch 59 is closed, drive motor 20 will start inoperation. When it has come up to speed, the start winding 56 isde-energized and switch 73 is closed by centrifugal mechanism 61. Theclosing of switch 73 completes the energizing circuit for heaters 26which thereupon start to heat the air as it is drawn into the drum 2 bythe blower 49.

At the same time, the biasing heater 7% is energized in series withresistances and 99. The resistance 99 is that which is selected forconnection in the circuit when the ambient temperature is between 70 andso that the provision of resistance 96) in the circuit has acompensating effect on biasing heater 78. The provision of intermediatevalue resistance 85 in the circuit also has a compensating effect onbiasing heater 78.

The condition of the thermostats 92 and 93 is not, of course, affectedby the progression of the drying cycle, and if, as is normally true, theambient temperature remains constant within a few degrees during thedrying cycle, resistance 99 Will continue to be the resistancedetermining the ambient temperature compensation effect on biasingheater 78. 7

As stated, the heater 26 is energized; after a period of suchenergization, in accordance with the efiect of biasing heater 78 asmodified by groups '79 and it the ther mostat 74 will trip in responseto a rise in the clothes temperature and will engage contact '75. Thisde-energizes heater 26 and energizes timer motor 63 which then continuesto operate until such time as the thermostatic element 74 resets andengages contact 76. At this point of course the heater 26 isre-energized and the timer motor 63 is de-energized. This causes thetemperature to rise again, and when the predetermined point is againreached the thermostat again causes de-energization of the heater andre-energization of the timer. It will be seen that this sequence willcontinue until such time as the timer has caused the cams to rotate tothe off position at which point all circuits within the dryer will beopened, and the sequence will be terminated, With the clothes within thedrum being completely dry.

After a predetermined length of timer operation, cam 65 will causeswitch 68 to close; this bypassing of resistance 85 will cause increasedpower to be available to bias heater 78 with the result that the clothestemperature causing tripping of thermostat '74 will be lowered. This isa highly desirable feature since with a clothes load which requires anintermediate temperature, such as ordinary cottons, it is desirable thattoward the end of the cycle the temperature be decreased to facilitatehandling of the clothes.

It will thus be observed that a drying cycle has been provided which inan economical manner, provides for compensation for the ambienttemperature (as claimed in the aforesaid Lynch application) and also bymy invention provides a heating effect tailored to the particular typeof load being dried While at the same time insuring that the temperaturewill decrease toward the end of the cycle to facilitate handling of theclothes.

If a relatively heavy load had been provided for drying, such as turkishtowels for instance, the manual control 7t} would have been set for amaximum time of operation of timer motor 63. This would have caused bothswitches 69 and 63 to be open originally (see FIGURE 4) and a highclothes temperature would have been required for tripping the thermostat74. As the timer motor operated the cams, the temperature would havefirst been decreased by the closing of switch 69 and then finally,toward the end of the cycle, by the closing of switch 68. If arelatively easily dried load such as delicate synthetics had been placedin the drum 2, the control 70 would have been set so that a relativelyshort amount of time was provided with switch 68 closed to provide a lowtemperature trip throughout the relatively brief period of operation.

It will thus be seen that, as an improvement of the basic concept of theaforesaid Lynch application, I provide an economical and elfectivesystem for tailoring the operation of the clothes drying machine 1 tothe type of clothes load. My invention, more specifically, resides inthe improvement to the aforesaid Lynch application which provides timercontrolled modification of the effectiveness of the biasing heater bymeans of a timer controlled switch in a circuit incorporating at leasttwo parallel conductors, the conductors providing one resistance whenthe switch is open and a different resistance when the switch is closed.

It will be recognized that, while a particular automatic sequence hasbeen described in which the operation of the heater and the timer arecompletely alternative to each other, many features of my invention willbe of value in other types of drying cycles including those whereoperation of the heater and timer is concurrent part of the time, andthose where the operation of the timer is continuous.

It will further be recognized that the biasing heater may be made tooperate continually as shown, or that its operation may be contingent onsome other factor such as the operation of the main heater 26. In thepresent embodiment it is deemed preferable that the operation of thebiasing heater be continuous, but it is readily conceivable that in somecases, particularly where the operation of the heaters and timer motoris not completely alternative in nature, it might be desirable to havethe biasing heater turned on and off at the same time as the mainheaters.

Another point to be noted is that while each group of conductors hasbeen shown to include three conductors including decreasing resistances,with switches in the two conductors having the lesser resistances, asfew as two and as many conductors as desired may be provided withoutdeparting from the invention. Also, variation in the resistancepresented by the conductors may be obtained other than by differentresistances with switch means opening the lesser resistance. Forinstance, if equal resistances are provided in each of two conductorswith a switch in one of them, the conductors will present a resistancewhen the switch is open which is twice as great as that which theypresent when the switch is closed; thus, exactly equal resistances mayeven be used to provide difierent resistances depending on the switchposition. In addition, the switch means need not necessarily be providedin the conductor having the lesser resistance but may, particularlywhere the resistances are not exceedingly low as in the case of thealmost short circuit provided by conductors 33 and 88 in the presentinvention, be provided in the conductor having the higher resistance,and a desirable compensating effect will still be obtained in responseto movement of the switch between open and closed positions.

While in accordance with the patent statutes I have described what atpresent is considered to be the preferred embodiment of my invention, itwill be obvious to those skilled in the art that various changes andmodifications may be made therein without departing from the invention,and it is therefore aimed in the appended claims to cover all suchequivalent variations as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a clothes drying machine, a clothes container, a main heaterpositioned to heat clothes in said container, thermostatic meanspositioned to be responsive to the temperature of clothes in saidcontainer, an electric resistance type biasing heater positioned inheating relationship to said thermostatic means, first switch meanscontrolling operation of said main heater, said thermostatic meanscausing said first switch means to open in response to a predeterminedhigh temperature, at least two parallel connected conductors in serieswith said biasing heater, at least one resistor and at least one secondswitch means connected in said conductors, said conductors providing agreater resistance when said second switch means is open and a lesserresistance when said second switch means is closed, manually presettableautomatic control means for automatically terminating operation of saidmain heater after a preselected period of operation of said controlmeans, said control means moving said second switch means to an openposition when said control means is set for a relatively long period ofoperation and to a closed position when said control means is set for arelatively short period of operation, whereby said biasing heater has asmaller effect on said thermostatic means when said relatively longoperation is selected and a relatively large effect on said thermostaticmeans when said relatively short operation is selected.

2 In a clothes drying machine, a clothes container, a mam heaterpositioned to heat clothes in said container,

ace:

thermostatic means positioned to be responsive to the temperature ofclothes in said container, an electric resistance type biasing heaterpositioned in heating relationship to said thermostatic means, firstswitch means controlling operation of said main heater, saidthermostatic means causing said first switch means to open in responseto a predetermined high temperature, at least two parallel connectedconductors in series with said biasing heater, each of said conductorshaving a different resistance included therein, the one of saidconductors including the lesser of said resistances further including asecond switch means in series with said lesser resistance, manuallypreettable automatic control means for automatically terminatingoperation of said main heater after a preselected period of operation ofsaid control means, said control means moving said second switch meansto an open position when said control means is set for a relatively longperiod of operation and to a closed position when said control means isset for a relatively short period of opera tion, whereby said biasingheater has a smaller effect on said thermostatic means when saidrelatively long operation is selected and a relatively large effect onsaid thermostatic means when said relatively short operation isselected.

3. The apparatus defined in claim 1 wherein, said control means isarranged so that when said relatively long period of operation isselected, said control means moves said second switch means to closedposition when the remaining length of operation of said control meanshas decreased to that which would be normally manually provided for saidrelatively short period of operation.

4. In a clothes drying machine, a clothes container, a main heaterpositioned to heat clothes in said container, first thermostatic meanspositioned to be responsive to the temperature of clothes in saidcontainer, an electric resistance type biasing heater positioned inheating relation to said thermostatic means, first switch meanscontrolling operation of said main heater, said first thermostatic meanscausing said first switch means to open in response to a predeterminedhigh temperature, two groups each including at least two parallelconnected conductors, said groups being connected in series with eachother and with said biasing heater, each group including at least oneresistor and one second switch means connected in the conductors of thatgroup, the conductors of each said group providing a greater resistancewhen said second switch means thereof is open and a lesser resistancewhen it is closed, second thermostatic means responsive to ambienttemperature to open said second switch means of one of said groups whenthe ambient temperature rises to a predetermined level, and manuallypresettable control means for variably limitiii ing the length ofoperation of a drying sequence, said control means opening said secondswitch means of the other or" said groups when a relatively long cycleof operation is selected and closing it when a relatively short cycle ofoperation is selected, whereby the effect of said biasing heater on saidfirst thermostatic means is variable both in accordance with ambienttemperature and with the length of the cycle selected.

5. The apparatus defined in claim 1 wherein said thermostatic meanscomprises a bimetallic element.

6. The apparatus defined in claim 1 including air circulating meansarranged to circulate ambient air over said heater and into saidcontainer, said thermostatic means being positioned to sense thetemperature of the air after it has contacted the clothes in saidcontainer.

7. The apparatus defined in claim 1 wherein said biasing resistance isconnected to operate continuously during a drying operation.

8. In a clothes drying machine, a clothes container, 21 main heaterpositioned to heat the clothes in said con tainer, thermostatic meanspositioned to be responsive to the temperature of clothes in saidcontainer, an electric resistance type biasing heater positioned inheating relationship to said thermostatic means, means controllingoperation of said main heater, said thermostatic means causing saidcontrolling means to shut said main heater off in response to apredetermined high temperature, at least two parallel connectedconductors in series with said biasing heater, at least one resistor andat least one switch means connected in said conductors, said conductorsproviding a greater resistance when said switch means is open and alesser resistance when said switch means is closed, manually presettable automatic control means for automatically terminating operation ofsaid main heater after a preselected period of operation of said controlmeans, said control means moving said switch means to an open positionwhen said manually presettable means is set for a relatively long periodof operation and to a closed position when said manually presettablemeans is set for a relatively short period of operation, whereby saidbiasing heater has a smaller efiect on said thermostatic means when saidrelatively long operation is selected and a relatively large effect onsaid thermostatic means when said relatively short operation isselected.

References Cited in the file of this patent UNITED STATES PATENTS2,790,114 Perkins Apr. 23, 1957 2,851,799 Worst Sept. 16, 1958 2,878,579Fuchs Mar. 24, 1959

